The present invention generally relates to a getter assembly for use in a vacuum display panel and more particularly, relates to a getter assembly for use in a vacuum display panel that consists of a non-evaporative getter and an evaporative getter positioned juxtaposed to each other such that ions emitted by the evaporative getter upon activation substantially shields the non-evaporative getter so that gases emitted by the non-evaporative getter upon activation does not affect a state of vacuum in the display panel.
In the fabrication of vacuum display devices such as FED (field emission device), PDD (plasma display device) and VFD (vacuum fluorescence display) etc., the degree of high vacuum achieved in a cavity of the device directly affects the quality and the lifetime of the device. Achieving a high vacuum in such devices is therefore an utmost important condition in fabricating devices of high quality and reliability. An effective means for reducing or eliminating residual gases in the cavity of the device, in turn, determines the degree of high vacuum that can be achieved. These gases may include H2, CO2, CO, H2 or any other gases emitted during the tip-off process from the molten glass and any other gases that tend to chemically absorb to the surfaces of the components in the device.
In most vacuum display devices, electrons are emitted from electron emitters such as microtips in a FED device for generating the display. When residual gases exist in the cavity of the device, the emitted electrons cause ionization of the residual gases which not only reduces the efficiency of the device, but also causes arcing problem resulting in serious damage to the device.
In the fabrication of vacuum display devices, a vacuum between about 10xe2x88x926 and 10xe2x88x927 Torr is normally required in order for the device to function properly. For instance, when a FED device is fabricated between two glass plates in which an upper glass plate is coated with a fluorescent coating on an inside surface and the lower glass plate is formed with a multiplicity of microtips on an inside surface, and after the upper and the lower glass plates are fused together by side panels of glass (by a fusing agent such as glass frit), at least one vent tube is left open for the lip final withdrawal of air and gases from the cavity by a vacuum pump. During the vacuum withdrawal process, the cavity is pumped by a high vacuum pump while the device baked at a temperature between 300xcx9c400xc2x0 C. for several hours. The pumping and the baking process normally get rid of most gases in the cavity, however, some gases which have strong absorption characteristics are attached to the device walls (especially at the bake temperature) and cannot be eliminated. Thus, after the vent tubes are sealed, the minute amount of residual gases cause a drop in the vacuum and furthermore, may cause ionization when bombarded by the electrons leading to severe damages to the device.
The residual gases in the cavity of a vacuum display device have been investigated to determine their sources or origin. One of the main sources of the residual gases is the molten glass material during the sealing or the tip-off of the vent tubes. Another major source of the residual gases is the material that is used to form the microtips, in the case of a field emission display device. It has been found that the microtip material tends to absorb gases that cannot be released at the normal bake temperature of 300xcx9c400xc2x0 C. Since it is impossible to completely eliminate the residual gases in a vacuum display device cavity after the device is sealed from the atmosphere, methods and devices for eliminating such residual gases after tip-off have been developed to resolve the outgassing problem occurred in the fabrication of such devices.
Getter materials are first developed to meet the needs of high vacuum during the process and the life of electron tubes many years ago. Pure barium encapsulated in iron or nickel tubes of small diameters was first utilized for such purpose. A compound of barium-thorium was also used for getters in the early development stage of the material. More recently developed getter materials can be classified into the categories of the evaporative getters (EG) and the non-evaporative getters (NEG). The most popular materials used as evaporative getters are Ba and Ti. For instance, Ba has been widely used in electronic applications such as CRT tubes. Ba is frequently used in the form of a compound of Ba/Al, such as BaAl4, an intermetallic compound. A typical Ba/Al compound is supplied commercially by the SAES Company of Milan, Italy.
In more recently developed electronic devices which utilize higher power, the high operating temperature and the high voltage make the use of evaporative type getter materials such as barium impossible. The non-evaporative getter materials become necessary and are developed for such use. A typical non-evaporative getter can be a thin layer of zirconium or titanium powder deposited on an anode strip. Metal alloys that contain zirconium or titanium such as a zirconium-aluminum alloy have also been developed for use as non-evaporative getters.
The getter materials normally require activation by an electrical current in order to function as a gas absorber. An activated and unsaturated getter surface readily reacts with residual gases that normally present in vacuum display devices which includes H2, H2O, CO, CO2, N2 and O2. When evaporative getters are utilized, activation is achieved by evaporating the getter material and thus creating a fresh unsaturated metallic film that readily absorbs gases by a chemical reaction. The function of the non-evaporative getters is more complex which normally involves an activation process carried out by properly heating the getter material and promoting a bulk diffusion of oxygen of a passivating surface layer until the surface is sufficiently clean to start absorbing the impinging gases.
The evaporative getter materials, i.e., frequently barium-containing materials, operate in a temperature range of 800xc2x0 C.xcx9c1200xc2x0 C. from an alloy that releases vapor of the metal getter material. The non-evaporative getter materials normally operate at different temperature ranges which consist of alloys based on titanium and/or zirconium. The evaporative and non-evaporative getter materials each having its own characteristics and benefits that are not achievable by the other. The combined use of EG and NEG therefore presents unique advantages that combines both that offered by the EG and the NEG. Even though the combination use of EG and NEG has been attempted by others, no effort has ever been made in the positioning of the two different types of getter materials in order to achieve an optimum result in absorbing residual gases in a vacuum device.
It is therefore an object of the present invention to provide a getter assembly for use in a vacuum display panel that does not have the drawbacks or shortcomings of the conventional getter assemblies.
It is another object of the present invention to provide a getter assembly for use in a vacuum display panel wherein the EG and NEG are uniquely positioned to compliment the function of each getter and to achieve an optimum result.
It is a further object of the present invention to provide a getter assembly for use in a vacuum display panel wherein an evaporative getter is positioned juxtaposed to a non-evaporative getter in a cavity of the device.
It is still another object of the present invention to provide a getter assembly for use in a vacuum display device wherein an evaporative getter and a non-evaporative getter are positioned juxtaposed to each other while each is connected to an electrode for activating by an electrical current.
It is still another object of the present invention to provide a getter assembly for use in a vacuum display device wherein an evaporative getter and a non-evaporative getter are both mounted inside a cavity of the device juxtaposed to each other.
It is yet another object of the present invention to provide a getter assembly for use in a vacuum display device wherein both an evaporative getter and a non-evaporative getter are mounted outside a cavity of the device in an enclosure which is in fluid communication with the cavity.
It is still another further object of the present invention to provide a getter assembly for use in a vacuum display device wherein a non-evaporative getter is activated by electrode means while an evaporative getter is activated by radial frequency (RF) induced current.
It is yet another flirther object of the present invention to provide a vacuum display panel that utilizes a getter assembly in a cavity of the panel that includes a non-evaporative getter and an evaporative getter positioned juxtaposed to each other such that ions emitted by the evaporative getter upon activation substantially shield the non-evaporative getter so that gases emitted by the non-evaporative getter when activated does not affect a vacuum state in the cavity of the display panel.
In accordance with the present invention, a getter assembly for use in a vacuum display panel is provided.
In a preferred embodiment, a getter assembly for a vacuum display panel is provided which includes a first getter of the non-evaporative type electrically connected to a first electrode for activating the getter, and a second getter of the evaporative type electrically connected to a second electrode for activating the getter, the second getter is positioned juxtaposed to the first getter and in such a way that ions emitted by the second getter upon activation substantially shield the first getter such that gases emitted by the first getter when activated does not affect a vacuum state in the vacuum display panel.
In the getter assembly for a vacuum display panel, the second getter of the evaporative type is positioned juxtaposed to the first getter of the non-evaporative type so that ions emitted by the second getter substantially surround the first getter. The second getter of the evaporative type forms a coating layer on the inside surfaces of an upper and a lower glass plate that form the vacuum display panel. The second getter of the evaporative type may be mounted on a tip portion of the second electrode for making electrical contact. The first getter and the second getter may be mounted in a cavity formed between two glass plates of the vacuum display panel. The first getter of the non-evaporative type may be mounted on a tip portion of the first electrode. The first and the second getter are activated through the first and the second electrode, respectively by an electrical current of less than 10 amp. The first getter of the non-evaporative type may be formed of a material including Ti or Zr. The second getter of the evaporative type may be formed of a material including Ba. The first and the second getter maintains a vacuum in the vacuum display panel of at least 10xe2x88x926 Torr when activated.
In another preferred embodiment, a getter assembly for a flat panel display (FPD) unit is provided which includes a first getter of the non-evaporative type mounted inside the insulating enclosure electrically connected to a feedthrough electrode for activation that houses the first getter, and a second getter of the evaporative type that is activated by a RF electrode coil mounted on the outside wall of an electrically insulating enclosure, the second getter may be positioned juxtaposed to the first getter such that ions emitted by the second getter upon activation shield the first getter and gases emitted by the first getter upon activation so as not to effect a vacuum pressure in the FPD unit by a factor of more than 100, the electrically insulating enclosure may be integrally attached to and in fluid communication with a cavity in the FPD unit.
In the getter assembly for a flat panel display unit, the electrically insulating enclosure may be a bell-shaped glass dome. The first getter of the non-evaporative type may be suspended in the electrically insulating enclosure in a spaced-apart relationship with the FPD unit. A coating layer may be formed by the second getter on an inside wall of the electrically insulating enclosure upon activation of the second getter. The second getter may be positioned suspended over the first getter in the electrically insulating enclosure. The electrically insulating enclosure may be fused to the FPD unit by glass frit. The electrically insulating enclosure may be in fluid communication with the cavity in the FPD unit through an aperture formed in a top wall of the FPD unit.
The present invention is further directed to a vacuum display panel that includes a top glass plate coated with a fluorescent material on an inside surface, a bottom glass plate that has a multiplicity of electron emitters formed on an inside surface, side panels joining the top and bottom glass plates forming a vacuum-tight cavity therein, and an electrically insulating enclosure integrally joined to the top glass plate, a cavity in the enclosure in fluid communication with the vacuum-tight cavity through an aperture provided in the top glass plate, wherein the electrically insulating enclosure further includes a getter assembly including a first non-evaporative getter and a second evaporative getter, the first non-evaporative getter is electrically connected to a first electrode for activation, the second evaporative getter is electrically connected to a second electrode for activation, the second getter may be positioned juxtaposed to the first getter and in such a way that ions emitted by the second getter upon activation substantially shield the first getter such that gases emitted by the first getter upon activation does not affect a vacuum state in the vacuum display panel.
In the vacuum display panel, the second getter of the evaporative type may be positioned juxtaposed to the first getter of the non-evaporative type such that ions emitted by the second getter substantially surround the first getter. The second getter of the evaporative type may form a coating layer on the inside surfaces of an upper and a lower glass plate that form the vacuum display panel. The second getter of the evaporative type may be mounted on a tip portion of the second electrode for making electrical contact. The first getter of the non-evaporative type may be mounted on a tip portion of the first electrode. The second getter of the evaporative type may be formed of a material including Ba. The first getter of the non-evaporative type may be formed of a material including Ti or Zr. The first and the second getter maintain a vacuum in the vacuum display panel of at least 10xe2x88x926 Torr when activated.